Various types of transparent and translucent glazing systems are available for the construction of sloped glazing, skylights, roofs, walls, and other architectural structures designed to pass light for daylighting interiors and other purposes. When using such glazing systems, it is often desirable to optimize the system's shading coefficient by reducing solar heat gain on hot summer days and during peak sunlight hours year round, while providing maximum light on cold winter days and when it is most needed. It is often necessary to minimize glare and direct sunlight at peak sunlight periods, to ensure comfort of those who occupy the space exposed to the glazing system. If architects and space planners can be liberated from the constraints of fixed light transmission, they can maximize interior daylight without the burden of unmanaged heat gain or discomforting glare.
Indeed, if the level of light passing through sloped glazing, skylights, roofs, walls, and other architectural structures designed to pass light can be simply and efficiently controlled, it will enable architects and space planners to design more efficient HVAC systems, by reducing or maximizing heat gain during those limited periods that require peak HVAC system performance and consequently reducing air conditioning and heating capacity requirements. Instead of investing in expensive over-capacity equipment to handle the limited excessive sunlight and cold days in any given year, the architects and space planners can rely on the glazed panel to reduce the peak demand times and therefore the maximum HVAC load capacity.
The known approaches to controlling the amount of light admitted through glazing systems, however, are limited and are generally difficult or expensive to construct and service. There is therefore a substantial need for a flexible, inexpensive, reliable and readily serviceable system for achieving this purpose.
Prior approaches to controlling the level of light passing through architectural structures have been of only limited usefulness. For example, louver blind assemblies using pivoting flexible members operable inside a chamber formed by a double-glazed window unit have been suggested for this purpose. Such louver blinds require substantial support of the flexible members which, additionally, must be controlled from both their distal and their proximal ends. Furthermore, louver blinds are difficult and expensive to assemble, apply, operate, maintain and replace, and cannot be readily adapted for use in non-vertical applications or in applications in which it is either desirable or necessary to control the flexible members from only one end.
U.S. Pat. No. 6,499,255 provides another, more recent approach to addressing this challenge. The '255 patent describes a unitary transparent or translucent panel of controllable radiation transmissivity comprising a plurality of rotatably-mounted radiation-blocking tubular members having at least one portion which is substantially opaque and means for rotating the radiation-blocking members to block out varying amounts of the radiation striking the panel by varying the area of the opaque portions presented to the incoming light. It is key to this structure that the radiation-blocking members be mounted in a series of adjacent segregated tubular cells which make up the unitary panel.
While the unitary panel described in the '255 patent represents an important advance in the art, it has some shortcomings. For example, adjacent tubular members cannot abut each other due to the intervening clear or transparent walls of the tubular cells. Thus, when the tubular members are in the fully closed position, light still passes through the clear or translucent material of the unblocked cell walls between the adjacent radiation-blocking members. Also, if a tubular member fails, the entire panel must be removed and replaced. This may be prohibitively complex and expensive in certain applications. Where the panels are part of a protected enclosure, removal of an entire panel will expose the interior of the enclosure to the exterior environment which can be problematic.
Additionally, in the design of the '255 patent the diameter of the radiation blocking members is constrained by the size of the cells—where circumstances make larger or smaller radiation-blocking members desirable or necessary due to economic or other reasons, the system of the '255 patent cannot accommodate them. For example, the maximum cell size available following the teaching of the '255 patent is 30 mm×30 mm due to manufacturing constraints in extruding the panels. Thus, a panel width of 1 meter by 30 mm in thickness or depth will require 33 tubular members as well as 33 related driven mechanisms which extend beyond the end of the panel. This is a very complex and expensive design which could be made substantially simpler and less expensive if the same result could be achieved with fewer larger diameter radiation-blocking members or with simpler drive mechanisms that preferably could be substantially contained within the area defined by the panel. Furthermore, the unitary cellular panel structure of the '255 patent resists bending, making it difficult to use the system in architectural applications where tight radius bends are required. Additionally, the cellular-panel structure has insulation, soundproofing and structural limitations arising from its maximum 30 mm thickness or depth that make its use less than ideal in applications calling for high insulation values, substantial soundproofing and long span construction. Finally, the unitary cellular panel structure of the '255 patent does not permit the use of different combinations of interior and exterior panel colors and finishes as required or desirable in many architectural applications.